Electric switching device comprising insulating parts reinforced with polyvinyl alcohol fibres

ABSTRACT

An electric switching device with insulating parts of mouldings, particularly extinguishing chamber plates in an arc extinguishing chamber, such mouldings being formed of resin binder reinforced with fiber material which is at least primarily fibers of polyvinyl alcohol or acetalised polyvinyl alcohol. The binder is an unsaturated resin converted into polymerised form.

[451 Mar. 26, 1974 United States Patent 11 1 Holmstriim 1 ELECTRICSWITCHING DEVICE [56] References Cited OTHER PUBLICATIONS COMPRISINGINSULATING PARTS REINFORCED WITH POLYVINYL ALCOHOL F IBRES 0 n om L n 5h w B W. nA .w mum.

\o D Z nw. Mm m. C H d kn kto mm HPS a r e t a V m .w m n 8 mm ww S o tn e V n l m 7 [73] Assignee: Allmanna Svenska Elektriska Aktiebolaget,Vasteras, Sweden Feb. 14, 1972 Primary Examiner-Robert S. Macon [57]ABSTRACT An electric switching device with insulatin [22] Filed:

mouldings, particularly extinguishing cham in an arc extinguishin formedof resin binder reinforced with which is at least primarily fl 2205/71Feb. 19, 1972 563/72 Foreign Application Priority Data or acetalisedpolyvinyl alcohol. The binder is an unsaturated resin converted intopolymerised form.

200/144 C, 200/149 A, 174/110 V,

174/137 B, 200/150 A Int. Cl. 110111 33/04 6 1 Dawmg Fgure 200/150 A,144 c, 149 A [58] Field of Search.........

1 ELECTRIC SWITCHING DEVICE COMPRISING INSULATING PARTS REINFORCEDWITI-I POLYVINYL ALCOHOL FIBRES BACKGROUND OF THE INVENTION 1. Field ofthe Invention The invention relates to an electric switching device andespecially a high voltage circuit breaker in which the insulating partsare subjected to the influence of electric arcs during operation.

2. The Prior Art Insulating parts which during operation come intocontact with electric arcs are subjected to high mechanical, electricaland thermal stresses. It is of decisive importance for the speration ofthe switching means that the material in said insulating parts issufficiently resistant to arcs so that the material is not burnt away totoo great an extent. The material must also have such properties thatthe influence of the arc does not give rise to polluted surfaces,primarily as a result of the formation of soot, and thus to creepagesparking.

-'It has proved extremely difficult at the same time to achievesufficient mechanical strengh and also sufficient resistance to electricarcs. Examples of switching devices where problems of the type describedarise are circuit breakers and contactors and also isolators havingextingushing chutes.

Furthermore, the requirements are permanently increasing for shortbreaking times for high voltage circuit breakers, i.e. that time fromthe moment when the breaker receives an opening impulse signal until themoment when the current is cut off. The increased requirements for shortbreaking times are due to the expansion of electric power transmissionnetworks and thus the increasing short-circuit powers. In order toachieve short breaking times it is important that the voltage strengthin the extinguishing chamber is built up so quickly that so calleddielectric re-ignition does not occur. The material in the insulatingparts which comes into contact with the arc is therefore very importantsince a flash-over is often caused by creepage currents along thesurfaces of the insulating parts.

Previously a great number of inorganic and organic insulating materialshave been used for said insulating parts. Recently, however, mouldedmaterial with binders of synthetic resin have been used to an increasingextent, such as polyester resins and epoxy resins with powdered andfibrous fillers. In order to satisfy the requrements of mechanical andthermal strength glass fibres have been principally used as fibrousfiller and reinforcing material. It is also known to use mouldings ofacrylate resins such as polymethyl methacrylate without filler.

However, it has been found that there are problems in using glass fibresas filler and reinforcing material. The problem have probably somethingto do with the considerable tendency to creepage current which heatedglass fibres have and with the fact that the glass is altered androughened at the high temperatures of the arc, which results in theglass retaining soot particles so that the dielectric strength of theinsulation will be very poor along the surface.

SUMMARY OF THE INVENTION According to the present invention it has beenfound possible while retaining the good mechanical and thermalproperties of the insulating parts which can be achieved with glassfibres as reinforcement, to considerably improve the resistance of theseinsulating parts to arcs. The improvement is achieved by the use of afibre material in the insulating parts which consists at leastsubstantially of polyvinyl alcohol fibres or acetalized polyvinylalcohol fibres. A likely explanation of the improvement achieved is thatpolyvinyl alcohol disintegrates at low temperatures to produce gases,for instance water vapour, which effectively keeps the are at a distancefrom the surface of the insulating parts and thus saves the surface fromthe direct influence of the arc. At the same time, the gas productioncontributes to extinguishing the arc and thus to shortening the durationof the arc.

The present invention relates more specifically to a switching devicehaving insulating parts of mouldings reinforced with fibre material,which are subjected to the influence of electric arcs and ischaracterised in that the fibre material consists at least substantiallyof polyvinyl alcohol fibres or acetalized polyvinyl alcohol fibres.

Polyvinyl alcohol fibre has been a commerical product at least since1950. In the following description the term polyvinyl alcohol fibresincludes not only polyvinyl alcohol fibres as such but also acetalizedpolyvinyl alcohol fibres, i.e. polyvinyl alcohol fibres which have beenacetalized.

When manufacturing mouldings according to the present invention,polyvinyl alcohol fibres can be used in the manner conventional forglass fibres, i.e. in the form of wool, short fibres or fibre strings,cloth and webs, together with a resinous binder. The reinforced productscan be produced by compression moulding compounds and injection mouldingcompounds, by moulding impregnated webs to laminates, by hand layup,fibre winding and centrifugal casting.

The length of the fibres in moulding compounds is suitable l mm,preferably 3 50 mm and in injection moulding compounds suitably l 50 mm,preferably l 10 mm. Their diameter is suitably l 50 mm.

The quantity of polyvinyl alcohol fibres in the finished mouldings issuitably 5 40, preferably 10 25 percent of the weight of the mouldings.

As examples of suitable binders for the moulding may be mentionedethylenically unsaturated polyester resins with methyl methacrylate,other acrylates or methacrylates, such as the monomers mentioned belowhaving several arcylate groups, as well as diallylphthalate or tirallylcyanurate as ethylenically unsaturated monomers in a quantity of 15 45percent of the weight of the polyester resin including the monomer,acrylate resins such as a mixture of on the one hand a linear acrylatepolymer, for example a polymer of methyl methacrylate, methyl acrylate,ethyl methacrylate or ethyl acrylate or a copolymer of two or more ofthese substances and, on the other hand, a monomer having sev' eralacrylate groups, for example ethylene glycol dimethacrylate,l,4-butanedisldimethacrylate, neopenthyl glycolYliYnethacrylate,diethylene glycol dimethacrylate, triethylene glycol dimethacrylate,tetraethylene glycol dimethacrylate, pentaethylene glycoldimethacrylate, hexaethylene glycol dimethacrylate and trimethylolpropane trimethacrylate or corresponding compounds in which themethacrylate groups have been replaced by acrylate groups and mixturesof two or more such monomers containing methcrylate or acrylate groups,at least partially polymerised diallylphthalate, epoxy resins withcuring agents of anhydride type such as hexahydrophthalic acidanhydride, carbamide resins and melamine resins. Particularly preferredare the acrylate resins mentioned and especially a mixture of a linearacrylate polymer of the type mentioned and a monomer in the form of amonomeric acrylate compound consisting of a polyethylene glycoldimethacrylate and/or diacrylate such as a dimetacrylate or diacrylateof diethylene glycol, triethylene glycol, tetraethylene glycol,pentaethylene glycol, hexaethylene glycol and heptaethylene glycol,possibly with an additive resin containing ethylenically unsaturatedgroups which are copolymerisable with the unsaturated groups in thepolyethylene glycol dimethacrylate or diacrylate. As examples of suchadditive resins may be mentioned unsaturated polyester resins, partiallypolymerised allyl esters, for example diallylphthalate anddiallylmaleate, acryl-modified, preferably cycloaliphatic epoxy resinsand unsaturated polybutadiene resins, for example having a molecularweight of 1,000 3,000 and containing approximately 85 percent of theunsaturated groups in 1,2 position. The quantity of linear acrylatepolymer should preferably be 25 percent and the quantity -of monomericacrylate compound about 65 90 percent of the total weight of thesesubstances. The quantity of additive resin should be at the most 25percent, i.e., 0 25 percent of the total weight of acrylate polymer,monomeric acrylate compound and additive resin. The quantity of binderis suitable 70 percent, preferably 50 percent of the weight of themoulding.

The unsaturated polyester resin may be of conventional type. It can beproduced in the normal manner by esterifying ethylenically unsaturatedand saturated, preferably aliphatio dicarboxylic acids or correspondinganhydrides with an equivalent quantity or a slight excess of abifunctional alcohol. As examples of unsaturated acids which can be usedfor this purpose may be mentioned maleic acid, fumaric acid, itaconicacid as such, or in the form of anhydrides. Examples of saturated acidswhich can be used are primarily adipic acid, sebacic acid, succinic acidas such or in the form of anhydrides. As examples of suitablebifunctional alcohols may be mentioned glycols such as ethylene glycol,propylene glycol and butylene glycol as well as polyglycols such asdiethylene glycol, triethylene glycol and dipropylene glycol.

The mouldings may also contain inorganic and organic powered filler,such as chalk, kaolin, dolomite, bauxite, mica powder, silica powder,zirconium dioxide, zirconium silicate, silicon carbide, aluminumtrihydrate, cellulose powder, polyacetal powder (polyoxymethylene), etc.The quantity of powder filler may be at the most 70, suitably l 70 andpreferably 15 60 percent of the weight of the moulding, i.e. the totalweight of the binder, fibrous material and powdered filler.

Besides polyvinyl alcohol fibres the mouldings may also contain otherfibrous material such as cotton, sisal fibres and asbestos to a totalweight of less than the weight of the polyvinyl alcohol fibres.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be furtherexplained by describing a number of embodiments by way of example withreference to the accompanying drawing which shows schematically a highvoltage circuit breaker of minimum liquid type with transverseextinguishing chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The circuit breaker shown has acylindrical extinguishing chamber 1 and a cylinder 2 concentric withthis, both of glass-fibre reinforced plastic. At the upper end of theseparts is a metallic cover 3 provided with a current terminal 4 connectedto the stationary contact 5 of the circuit breaker. The movable contact6 of the breaker consists of a contact plug which can be displacedwithin the current collector 7 and through an arcing chamber 8 inrelation to the stationary contact 5 arranged in the upper part of thearcing chamber. A number of extinguishing chamber plates 9 are arrangedhorizontally in the arching chamber. The lower surface of each plate isfiat over the entire area of the plate. Each plate has a central hole 12for the movable contact and a substantially radial groove at the topwhich extends from the hole 12 to an exhaust channel 11 inside the wallof the extinguishing chamber. Said groove thus forms a horizontal gap 10(transverse blowing gap) which leads from the arcing chamber 8 and opensout into the exhaust channel 11. The thickness of the material of eachplate is greater towards the exhaust channel 11, i.e. in those partswhich surround and are higher than the radial groove than towards theopposite end from the hole 12, so that there are open spaces between theplates towards the latter direction, as can be seen from the drawing.The plates are stacked on each other, in close contact with each otherwhere the thickness of the plates is greatest (behind the plane shown inthe drawing). In order to protect the inner wall of the extinguishingchamber against the hot gases blown out through the gaps 10, acylindrical screen 17 of moulded material reinforced with polyvinylalcohol fibres may be arranged inside the cylinder 1 along a part of itscircumference. The binder in this material may be of the same sort asthat mentioned for the insulating parts subjected to the influence ofelectric arcs, as for the plates 9. The inner wall of the extinguishingchamber cylinder 1 may also be protected by giving the plates 9 of theextinguishing chamber the same diameter as the inner diameter of theextinguishing chamber cylinder and shaping each plate with a holerunning in axial direction spaced from the periphery and thus from thewall of the extinguishing chamber. The holes in the plates stacked ontop of each other thus together form an exhaust channel corresponding tothe exhaust channel 11 in the drawing.

The circuit breaker is filled with liquid, for example oil, to the level13 in the cover. A porcelain insulator 14 is arranged around thecylinder 2. During a breaking process the oil in the arc zone isvaporized due to the influence of the arc and an extremely high pressureis thus built up in the arcing chamber 8. As the transverse blastinggaps 10 are exposed by the movable contact 6, the arc is subjected to apowerful flow of oil and gas which cools and deionises the arc. In orderto ensure that small currents are broken, a number of liquid pockets 15may be arranged in the lower part of the extinguishing chamber.

In the arrangement shown the extinguishing chamber plates 9 aresubjected to the influence of an arc. Ac-

cording to the present invention these plates are made of mouldingsreinforced with polyvinyl alcohol fibres. In the following examples willbe given for their manufacture.

Example 1 A moulding compound is manufactured of the followingcomponents:

30 parts by weight of an unsaturated polyester resin manufactured inconventional manner from 2 mols maleic acid anhydride, 1 mol succinicacid and 3.3 mols ethylene glycol and mixing 70 percent by weight of thereaction product thus obtained with 30 percent by weight methylmethacrylate. Esterifying is carried out at 165 -l90C to an acid numberof 35.

0.5 parts by weight benzoyl peroxide 1.5 parts by weight zinc stearate20 parts by weight polyvinyl alcohol fibres having a length of 15 mm 95parts by weight zirconium dioxide The components are kneaded together toa homogenous pulp similar to cotton waste. This is compression mouldedand cured in the mould at a pressure of 100 kg/cm and a temperature of140C for 4 minutes. Example 2 A moulding compound is manufactured of thefollowing components:

30 parts by weight of an acrylate resin consisting of 75 parts by weighttriethylene glycol dimethacrylate and 25 percent by weight polymerisedmethyl methacrylate having a molecular weight of 140,000

0.5 parts by weight butyl perbenzoate 15 parts by weight polyvinylalcohol fibres having a length of 15 mm 5 parts by weight cellulosepowder 1.5 parts by weight zinc stearate 48 parts by weight kaolin Themoulding compound is manufactured and moulded in the same way as thecompound described in Example 1. Example 3 An injection mouldingcompound is manufactured of the following components:

36 parts by weight pre-polymerized diallylphthalate with a melting pointof 95C 4 parts by weight monomeric diallylphthalate 1 parts by weightbutyl perbenzoate parts by weight polyvinyl alcohol fibres having alength of 3 mm 48 parts by weight kaolin The components are mixed welland rolled together in a rolling mill at 80 90C. After cooling therolled product is ground to particles with a size of approximately 3 mm.The compound can be transfer moulded and injection moulded at atemperature of 160C. A suitable pressure is 100 kg/cm suitable transferpres sure 300 kg/cm suitable curing time 150 s and suitable injectiontime s. Example 4 A compound is manufactured of the followingcomponents:

50 parts by weight of a melamin-formaldehyde resin (2 mols formaldehydeper mol melamine) 30 parts by weight calcium carbonate 2 parts by weightzinc stearate 18 parts by weight polyvinyl alcohol fibres having alength of 15 mm The components are kneaded together in a sigma kneader.When the water has evaporated in the furnace at approximately 50C, theproduct obtained is ground to particles having a size of approximately 3mm. The compound is suitable for compression moulding, injectionmoulding and transfer moulding. It can be handled under the sameconditions as the'compound described in Example 3.

Example 5 A moulding compound is manufactured of the followingcomponents:

35 parts by weight of an epoxy resin containing of a mixture of 51percent by weight of a cycloaliphatic epoxy resin part with an epoxycontent of 6.2 equ./kg and a viscosity of 1.5- 10 cP at 25C, 48.5percent weight of a curing agent part consisting of a hexahydrophthalicacid anhydride and 0.5 percent by weight of an acceleration partconsisting of benzyl dimethylamine 10 parts by Weight polyvinyl alcoholfibres having a length of 10 mm 2 parts by weight zinc stearate 30 partsby weight aluminum trihydrate 23 parts by weight zirconium silicate Thecomponents are kneaded together at around C. The doughy compound thusobtained is cured at a temperature of 170C and a pressure of kg/cmExample 6 A moulding compound is manufactured of the followingcomponents:

30 parts by weight of a resin consisting of 60 parts by weight ofpercent tetraethylene glycol dimetacrylate, 25 percent by weight of acopolymerisate of equal parts methyl acrylate and methyl methacrylatehaving a molecular weight of 130,000 and 15 percent by weight of anunsaturated polyester resin produced in conventional manner fromdiethylene glycol and maleic acid anhydride using 1.1 mol diethyleneglycol per mol maleic acid, by boiling at C to an acid number of 40.

0.5 parts by weight benzoyl peroxide 12 parts by weight polyvinylalcohol fibres having a length of 25 mm 20 parts by weight cellulosepowder having a particle size of around 100 microns The mouldingcompound is manufactured and moulded in the same was as the compounddescribed in Example 1.

Example 7 A moulding compound is manufactured and moulded in the mannerstated in Example 6 with the exception that the unsaturated polyesterresin stated there is replaced by an equal amount of prepolymeriseddiallylphthalate (for example DAPON from Food Machinery Corporation,USA).

The compounds described in Example 1 7 can be used not only formanufacturing extinguishing chamber plates in high voltage circuitbreakers, but also for manufacturing other insulating parts which aresubjected to the influence of electric arcs in switching devices ofdifferent types, such as extinguishing chutes in contactors andisolators.

1 claim:

1. Electric switching device having at least one insulating part ofmouldings of a resin binder reinforced with fibre material, which issubjected to influence of electric arcs, in which the fibre materialconsists essentially of fibres of polyvinyl alcohol fibres or acetalizedpolyvinyl alcohol.

2. Electric switching device according to claim 1, consisting of a highvoltage circuit breaker comprising an extinguishing chamber, in whichthe insulating part constitutes an extinguishing chamber plate in theextinguishing chamber.

3. Electric switching device according to claim 2, in which the binderconsists essentially of an unsaturated polyester resin converted intocured form and containing an acrylate or methacrylate as monomer.

4. Electric switching device according to claim 2, in which the binderconsists essentially of a mixture of a linear acrylate polymer and atleast one monomer comprising a polyethylene glycol dimethacrylate orpolyethylene glycol diacrylate, converted into polymerised form.

5. Electric switching device according to claim 4, in which the contentof linear acrylate polymer constitutes 1O 35 percent and the content ofmonomer 65 percent of the total weight of these substances.

6. Electric switching device according to claim 4, in which the bindercontains an additive resin containing ethylenically unsaturated groupswhich are copolymerisable with the unsaturated groups in thepolyethylene glycol dimethacrylate or diacrylate, the quantity ofadditive resin being at the most 25 percent of the total weight ofacrylate polymer, monomeric acrylate compound and additive resin.

2. Electric switching device according to claim 1, consisting of a highvoltage circuit breaker comprising an extinguishing chamber, in whichthe insulating part constitutes an extinguishing chamber plate in theextinguishing chamber.
 3. Electric switching device according to claim2, in which the binder consists essentially of an unsaturated polyesterresin converted into cured form and containing an acrylate ormethacrylate as monomer.
 4. Electric switching device according to claim2, in which the binder consists essentially of a mixture of a linearacrylate polymer and at least one monomer comprising a polyethyleneglycol dimethacrylate or polyethylene glycol diacrylate, converted intopolymerised form.
 5. Electric switching device according to claim 4, inwhich the content of linear acrylate polymer constitutes 10 - 35 percentand the content of monomer 65 - 90 percent of the total weight of thesesubstances.
 6. Electric switching device according to claim 4, in whichthe binder contains an additive resin containing ethylenicallyunsaturated groups which are copolymerisable with the unsaturated groupsin the polyethylene glycol dimethacrylate or diacrylate, the quantity ofadditive resin being at the most 25 percent of the total weight ofacrylate polymer, monomeric acrylate compound and additive resin.